1. Field of the Invention
This invention relates to diamond drag bits.
More particularly, this invention relates to a means to cool and clean each diamond insert stud standing-off from the face of a diamond drag bit.
2. Description of the Prior Art
Conventional synthetic diamond composite blanks typically are cemented, brazed, or sintered to an insert stud. The diamond layer is generally composed of a polycrystalline material joined to a substrate layer of tungsten carbide material. A synthetic diamond blank of the above description is, for example, manufactured by the Specialty Material Department of General Electric Company of Worthington, Ohio. The foregoing synthetic diamond composite blanks go by the trademark name of Stratapax drill blanks. The Stratapax blanks are generally brazed to the insert stud bodies, the face of the blanks being aligned about 20.degree. with respect to the axis of the body of the stud insert. The studs are typically strategically placed within the face of the diamond drag bits to optimize the cutting action of the drag bit as it is advanced in a borehole. A series of channels or hydraulic passages are generally formed in the drag bit face to provide hydraulic fluid or "mud" to cool and clean each of the studs mounted within the face of the drag bit. These hydraulic channels and passages may be plugged by the cuttings in the bottom of the borehole. For example, the drag bit may gum up when passing through softer formations, thus plugging some of the hydraulic passages in the bit face. If this happens, the individual studs mounted in the drag bit are ineffective and may become overheated and damaged due to lack of cooling.
By providing hydraulic passages in each stud body, each insert stud then has its own supply of hydraulic mud to cool and clean each insert. The hydraulic passage exits each stud in front of the synthetic diamond cutting face of the insert to assure a supply of mud to cool the cutting face of the insert. By providing hydraulic passages in each of the stud bodies, rather than providing separate hydraulic passages in the face of the drag bit body, the drag bit body then is much stronger. This is true because the interference fit holes formed in the face of the drag bits also include the hydraulic passages to cool the bit. A fluid communication link between the hydraulic chamber formed by the drag bit body and the passage formed in each of the stud inserts is thus maintained without the need for separate hydraulic passages or nozzles in the drag bit. The drilling operation wherein the interference fit stud holes are drilled can now be a two-step operation. In the first step, the interference hole is drilled. Secondly, the hydraulic passage is drilled between the bottom of the interference hole and the mud chamber formed by the bit body, this passage being so positioned to align with the passage in the stud. The fabrication process then is much simpler in that both holes are formed by the drag bit in close proximity, one from the other. The drag bit body then is much stronger and tougher since it is not penetrated by a multiplicity of hydraulic passages.
This invention eliminates the need for multiple hydraulic passages in the face of a synthetic diamond drag bit by providing hydraulic passages within the same interference fit hole that the studs are fitted within, each of the studs having hydraulic passages formed therein.